Patent GB-983148-A (GB)
Title: Engine fuel supply systems
Inventor: TYLER STANLEY RALPH
IPC: F02C9/16
Filed: 1961-02-28
Abstract: 983,148. Gas turbine plant. DOWTY FUEL SYSTEMS Ltd. Feb. 22, 1962 [Feb. 28, 1961], No. 7345/61. Heading F1G. [Also in Division G3] General. A gas turbine fuel system in which overfuelling during acceleration is prevented has a first and second control means adjusting fuel flow to the engine, and safety means responsive to failure of one control means to disconnect the latter. The system includes a boost pump 2, Fig. 1, which supplies a main pump 6 through an electric flow meter 4 and a filter 5, which pump 6 is connected to spill burners 9 via a minimum pressure valve 8. Spill from the burners 9 passes through a spring-closed spill valve 13 to the inlet of the main pump 6, the position of the valve 13 being determined by an all speed governor control 17 and an acceleration control 18 embodying the fail-safe means. In a modification, an acceleration detector Fig. 2, is disposed upstream of the burners 9. Speed governor control. A flyball governor 19, Fig. 1 driven at a speed proportional to that of the engine is connected to a spool valve 22 that acts on one arm of a lever 23 in opposition to a rod 27, the position of which is adjustable from the pilots lever 28; the rod is loaded by a spring- urged lever 29. The position of the valve 22 determines that of a servopiston 37 having a rod 38 pivoted to a lever 39, the free end of which abuts the stem of the spill valve 13; the other arm of lever 23 carries a spring 42 which acts upon the rod 38. In the modification, the all-speed governor 85, Fig. 2, is as described in Specification 694,318 and controls the position of a servopiston 101 attached to the spill valve 13. Acceleration control. An electronic computer 44, Fig. 1, which calculates how much fuel in excess of that actually supplied could be fed to the engine without causing stall or surge, takes signals from the flow meter 4, an engine speed indicator 45, and compressor inlet and outlet pressure transducers 46, 47; the computer output signal is transmitted along a line 205 to means controlling a flapper 49 between two orifices supplied through restrictions 54, 55 and controlling a servopiston 57, the rod of which abuts the stem of the spill valve 13. In the modification, the two computer output signals are conveyed by lines 102, 103, Fig. 2, to resistors 104, 105 acting as a potentiometer, the sliding contact 107 of which is carried by a rod 108; an electric motor 112 is connected between the line 102 and the contact 107 through an amplifier. Rod 108 is part of a servopiston 113, the cylinder of which is open to the pressure duct 94 via a passage 115 and a restrictor 116, and to conduit 119 in the spill valve 13 by a passage 117 and a restrictor 118. Conduit 119 communicates with the rod side of servopiston 101 through a restrictor 121 and filter 122 as well as with a low pressure zone 123. Fail safe mechanism. Downward motion of the servopiston 37, Fig. 1, actuates a switch 61 to energize a relay S1 whilst another relay S2 is supplied with an acceleration signal from the computer via a line 206. The line 205 includes parallel branches 62, 63, the former incorporating normally closed and open switches 65, 67 in relay S2; switches 66, 67 are in circuit with a further relay S3, a manually operable switch S4, a warning light 68 and an electrically operated valve 69, which upon actuation connects both sides of a dashpot 71 through a restriction, and since the dashpot 71 is attached to the rod 27 imparts increased resistance to movement of the pilot lever 28. The relay S3 controls a switch 73 in line 205 with a manually disengageable latch 74. In the modification motor 112, Fig. 2, drives a clutch 124 via gearing 125, which clutch is connected to a cam 12 that controls flow from a duct 141 and hence the position of a servopiston 132 which in turn controls a member 134 and determines the flow from conduit 119. Spring-loaded member 147 assumes a given position for a given force of fuel flow from the positive displacement engine-driven pump 6 and hence is responsible to acceleration; the member 147 is connected to piston 153 in a cylinder 152 open on one side of the piston to pressure via a duct 154, which side is also connected by a duct 155 to a spring-loaded diaphragm 156 acting on a lever 144. The cylinder part on the other side of the piston 153 leads via a duct 159 to the other side of the diaphragm 156; the piston 153 embodies a restrictor 161 and a relief valve 162. The lever 144, which controls the clutch operation is coupled to the rod 108 by a spring 146. Operation. Upon the pilot selecting an acceleration, the resulting signal from the computer actuates relay S2, Fig. 1, before the acceleration selected signal actuates relay S1, since the latter incorporates a delay device, so opening switch 67 and closing switch 65. Operation of relay S1 then opens switch 64 and closes switch 66 so that the flapper 49 is controlled via line 205. Should acceleration not occur, switch 67 will remain closed and switch 65 open so that the valve 69 is energized and the warning light 68 illuminated. No signals can be transmitted along line 205 until the latch 74 is released to enable the switch 73 to close. In the modification, movement of the lever 88, Fig. 2, to cause acceleration produces a motion of the servopiston 101 through operation of the governor 85 which urges the spill valve in a closing direction whereupon the end of conduit 119 approaches member 134 restricting the flow through conduit 119, building up pressure in passage 117, and trans- 1ating servopiston 113 towards lever 144; the potentiometer 104, 105 transmits a signal to motor 112 which rotates cam 126 anticlockwise and moves member 134 away from conduit 119. The voltage across the motor 112 is proportional to the permissable increase in fuel when accelerating and the member 134 is positioned to prevent this increase being exceeded. Closing of the spill valve 13 results in more fuel being required from pump 6, which thereby forces the piston 153 to the right producing a higher pressure in duct 159 so urging the diaphragm 156 and lever 144 downwards. The restrictor 118 ensures that the pressurization of diaphragm 156 occurs before the servopiston 113 reaches the limit of its movement. When the system is in equilibrium the contact 107 is in the position shown and no voltage signal is supplied to the motor 112. Should a selected acceleration not occur the output from the pump 6 does not increase and piston 153 remains stationary so that upward movement of the servopiston 113 causes the lever 144 to hinge in a corresponding direction and disconnect the clutch 124, whereupon a spring 129 rotates the cam 126 anticlockwise to elevate the member 134 and render the acceleration control inoperative at the same time illuminating a warning light 171. The clutch can only be re-connected upon releasing a latch 165. Specification 694,318 is referred to.